1. Field
The embodiments relate to managing transmissions between devices
2. Description of the Related Art
An adaptor or multi-channel protocol controller enables a device coupled to the adaptor to communicate with one or more connected end devices over a connection according to a storage interconnect architecture, also known as a hardware interface, where a storage interconnect architecture defines a standard way to communicate and recognize such communications, such as Serial Attached Small Computer System Interface (SCSI) (SAS), Serial Advanced Technology Attachment (SATA), Fibre Channel, etc. Further details on the Fibre Channel architecture are described in the technology specification “Fibre Channel Framing and Signaling Interface”, document no. ISO/IEC AWI 14165-25. Devices may communicate through a cable or through etched paths on a printed circuit board when the devices are embedded on the printed circuit board. These storage interconnect architectures allow a device to maintain one or more connections with end devices through a direct connection to the end device or through one or more expanders. In the SAS/SATA architecture, a SAS port is comprised of one or more SAS PHYs, where each SAS PHY interfaces a physical layer, i.e., the physical interface or connection, and a SAS link layer having multiple protocol link layer. Communications from the SAS PHYs in a port are processed by the transport layers for that port. There is one transport layer for each SAS port to interface with each type of application layer supported by the port. A “PHY” as defined in the SAS protocol is a device object that is used to interface to other devices and a physical interface Further details on the SAS architecture for devices and expanders is described in the technology specification “Information Technology—Serial Attached SCSI (SAS)”, reference no. ISO/IEC 14776-150:200x and ANSI INCITS.***:200x PHY layer (Jul. 9, 2003), published by ANSI and details on the SATA architecture are described in the technology specification “Serial ATA: High Speed Serialized AT Attachment” Rev. 1.0A (January 2003).
An expander is a device that facilitates communication and provides for routing among multiple SAS devices, where multiple SAS devices and additional expanders connect to the ports on the expander, where each port has one or more SAS PHYs and corresponding physical interfaces. The expander also extends the distance of the connection between SAS devices. With an expander, a device connecting to a SAS PHY on the expander may be routed to another expander PHY connected to a SAS device. Further details on the SAS architecture for devices and expanders is described in the technology specification “Information Technology—Serial Attached SCSI (SAS)”, reference no. ISO/IEC 14776-150:200x and ANSI INCITS.***:200x PHY layer (Jul. 9, 2003), published by ANSI, referred to herein as the “SAS Specification”.
A port in an adaptor or expander contains one or more PHYs. Ports in a device are associated with PHYs based on the configuration that occurs during an identification transmission. An identification transmission are those one or more transmissions a device initiates to inform a connected device of information on the interface. A port is assigned one or more PHYs within a device for those PHYs within that device that are configured to use the same SAS address during the identification sequence and that connect to attached PHYs that also transmit the same address during the identification sequence. A wide port has multiple PHYs and a narrow port has only one PHY. A wide link comprises the set of physical links that connect the PHYs of a wide port to the corresponding PHYs in the corresponding remote wide port and a narrow link is the physical link that attaches a narrow port to a corresponding remote narrow port.
An interface is a physical or logical component that is connected to another interface on the same or a different device. The term interface may include interfaces other than PHY interfaces. A wide port comprises a port assigned multiple interfaces, where one or more interfaces may be assigned to a port. An interface address, such as the SAS address, comprises an address or identifier assigned to one or more interfaces.
The SAS specification provides two expander types, a fanout expander and an edge expander. A fanout expander may be located between edge expanders. An edge expander PHY connects to a fanout expander PHY, and each fanout expander PHY may connect to a separate edge expander, which edge expander connects to end devices. However, in the current SAS specification, there can only be one fanout expander in a domain. A domain comprises all devices that can be reached through an initiator port, where the port may connect to multiple target devices through one or more expanders or directly. Further, each edge expander device set shall not be attached to more than one fanout expander device. An edge expander device set may be attached to one other edge expander device set if that is the only other edge expander device set in the domain and there are no fanout expander devices in the domain.
For instance, a SAS initiator PHY may connect to an edge expander PHY. If that edge expander connects to another edge expander, then according to the SAS specification, the second edge expander must connect to end devices. Each expander extends the distance of a connection by eight meters. Thus, adding two expanders between an initiator and target devices extends the connection from eight meters to 24 meters. If an initiator connects to an edge expander, which connects to a fanout device, which then connects to one or more edge expander which connect to end devices, then the distance of the connection between an initiator and target has been extended from eight meters to 32 meters, where in the SAS Specification 32 meters is the maximum distance between SAS end devices.